大景深成像技术及其相移现象的控制

Large depth of field imaging technology & it's phase shift control

为了探讨三次方位相板在大景深CCD衍射受限成像系统中的作用和分析由三次方位相板引起的成像相移现象,采用原理对比分析及仿真实验的方法,得到了轴向离焦参数ψ和位相板系数α与成像系统调制传递函数及成像相移量s的关系函数,以及物方离焦量w为波长的0,50,150,300倍时普通成像系统与大景深成像系统的轮辐成像图。分析及实验结果表明,位相板以降低系统光学传递函数对轴向离焦量敏感程度的方式实现大景深成像,同时必然引起成像相移,且相移大小与景深放大倍数及位相板系数间存在一定对应关系。而适当控制景深放大倍数并合理选择位相板系数能够有效减小成像相移,获得满意的成像质量。

The role of cubic phase plate in large-depth-of-field diffraction limited system with CCD detector was discussed and the special phase shift phenomena caused by the cubic phase plate was studied. Mathematic functions indicating the relation between axial desfocus parameter ψ,cubic phase plate shape constant α and modulation transfer function（MTF） and image shift variable s were deduced. Spoke images for standard imaging system and that with large depth of field were shown when defocus variable w equals to 0,50,150 and 300 times wavelength respectively. Changing optical transfer function and reducing its sensitivity to axial defocus parameter, depth of field for imaging system was enlarged. Along with its enlargement, phase shift appeared simultaneously, which is related with both the extending ratio for depth of field and the constant for cubic phase plate. Thus phase shift could be very small and a satisfactory image might be achieved when the extending ratio was limited to a certain suitable range and a reasonable constant for cubic phase plate was chosen.